The present invention refers to a flameholder device for afterburners in gas turbine engines with a cooling air fan of by-pass type, comprising a plurality of air-cooled radial flameholder means which at their radially outer end are mounted to the afterburner casing and connected to the cooling air bypass duct and have a longitudinal air channel which ends at the radially inner end of said flameholder means, at which end is arranged a circumferentially extending arcuate flameholder gutter of generally V-shape in cross-section and with the open end of the xe2x80x9cVxe2x80x9d facing down-stream.
Particularly in military aircraft gas turbine engines are often used afterburners for providing a temporary additional thrust. In said afterburner is combusted a mixture of fuel, hot core air from the core engine and cooler air from the by-pass duct. For obtaining ignition and combustion there must be present a stable zone with low gas flow speeds and for that purpose flameholder means are used since long. When the temperature of the afterburner is very high, particularly when ignited, the flameholder means are subjected to a very severe environment. Despite this fact the flameholder means mostly are non-cooled and therefore have a limited service life. Cooling of the flameholder means has been suggested and implied the solution of many problems but instead also created new problems since the differences in temperature between various portions of the flameholder means may give reason to low-cycle fatigue which reduces the service life substantially. As examples of prior air-cooled flameholder means it might be referred to i.e. U.S. Pat. Nos. 5,396,761 and 5,396,763 and FR-2 709 342.
Thus the great thermal load on the flameholder means causes their service life to be short and therefore they must be subjected to maintenance and often exchange at short time intervals. In doing so, the whole engine usually need to be dismantled from the aircraft which is both time-consuming and expensive as well as not particularly adapted for field service in military applications. In the structures according to the above-mentioned prior art the flameholder means are mounted to the external engine casing by means of bolts which requires that said casing has to be reinforced which will make it heavier and that is a severe drawback. The bolt connections also contribute to the time consumption in maintenance and exchange.
In the prior construction known from U.S. Pat. No. 5,396,761 the flameholder means support at their radially inner end a transverse gutter-shaped shield means which together with the adjacent means form a circumferential supplemental shield assembly.
The object of the present invention is to suggest an improved design of a flameholder device of the aforementioned kind and said invention is distinguished substantially in that the flameholder means at their radially outer ends each are pivotably and releasably mounted to the afterburner casing on a tangential axis and in that the gutters of the respective flameholder means are formed as a common integral annular supporting and load-carrying body.
Owing to the invention it is now achieved that the flameholder means at their radially outer end no longer are secured to the edging casing by a rigid bolt connection but by means of a pivot pin so as to take no moment and to allow increased movability during the expansion of the flame tube of the engine and an improved distribution of the transfer of load from the flameholder device in its entirety to the outer casing of engine. The common annular body, namely, will distribute the stresses to all the flameholder means and hence to the engine casing which is very advantageous. Finally, the mounting of the flameholder means on a pivot pin provides that in maintenance and exchange said pins easily are removed and the whole flameholder device dismantled without need to remove the whole engine from the aircraft. Should also each flameholder means be mounted to the common annular body by means of similar pin connection said means also may be easily exchanged individually if desired.
In a flameholder device of this kind it is also a problem to reliably obtain the ignition of the afterburner under certain parts of the flight envelope, particularly when flying at high altitude.
A further development of the present invention now has for an object to provide a solution of this problem and suggest a design of the flameholder means which assures a reliable ignition of the afterburner during all conditions of operations, still at low manufacturing costs. Said embodiment is substantially distinguished in that within the flameholder means is arranged a longitudinal evaporator tube which at its radially inner end opens adjacent the inner end of the flameholder means and the radially outer end with its mouth is substantially facing the meeting core flow of the gas turbine, upstream of which evaporator tube end being mounted a fuel spreader for spraying fuel into said tube mouth, and the pressure within the forward end of the flameholder means being selected to be higher than the pressure inside the evaporator tube, and in that at some distance inwardly of the rear wall of the flameholder means, as seen in the main flow direction, is located a guide wall which delimits a rear cooling air duct, into which at the radially inner end of the flameholder means, the fan air flowing around the evaporator tube is directed and which debouches at the radially outer end of the flameholder means.
Owing to said features it is now obtained in a very simple way a highly improved cooling effect on the flameholder means without any risks for difficulties when reigniting the afterburner, particularly at high altitudes. This is due to the separation of the cooling and evaporation functions of the flameholder means.